The field of the invention pertains to antenna towers and, in particular, to towers for cellular phone antennas, sometimes popularly known as cell towers. Cell towers commonly are constructed in one of two forms. Either the towers are constructed of open steel truss work or a single hollow tube of welded steel typically referred to as a monopole. In both varieties, the towers are fastened to a concrete base and gracefully taper upwardly more than 100 feet to sometimes 220 feet. Cellular telephone antennas are quite massive in appearance in comparison with radio and other common antennas; therefore, considerable windloading is applied to a cell tower by the one or two antennas normally installed.
The popularity of cellular telephones has resulted in a demand for additional capacity and, therefore, a demand for additional cellular telephone antennas and cell towers; however, cell towers are expensive to install and considered very unaesthetic by the general public. As a result, there is a demand for devices to reinforce existing cell towers to thereby permit installation of additional cellular telephone antennas. Examples of monopole cell towers and cellular telephone antennas are disclosed in U.S. Pat. No. 5,333,436 and U.S. Pat. No. 6,028,566. The former reveals a modular bolt-together form of cell tower with a massive antenna. The latter reveals the size and complexity of a cellular telephone antenna thereby emphasizing the bending moment that may be applied to the cell tower by the windage of the antenna. U.S. Pat. No. 6,173,537 illustrates a monopole with paraboloidal antennas commonly in use and likewise capable of producing considerable windage.
Numerous attempts have been made to reinforce monopole cell towers and previous antenna and utility towers prior to the development of cellular telephones. U.S. Pat. No. 6,453,636 discloses a plurality of half cylinders bolted about a monopole tower. Likewise, U.S. Pat. Appln. Pub. No. US2002/0056250 discloses a plurality of half cylinders bolted about a monopole tower. In contrast, U.S. Pat. Appln. Pub. No. US2002/0140621 discloses a concrete fill placed inside the monopole to provide more stiffening in compression to the monopole and the addition of external steel plates to the monopole.
U.S. Pat. Appln. Pub. No. US2002/0170261 discloses a plurality of square tubes attached by straps to the exterior of the monopole tower. The straps include square tubing collars through which the square tubing passes. U.S. Pat. Appln. Pub. No. US2002/0176951 discloses a load redistribution mechanism generally about the base of the monopole tower. U.S. Pat. Appln. Pub. No. US2003/0000165 discloses a precast post-tensioned segmental pole system wherein the post tensioning cables are located within the hollow interior of the tower. Fiber reinforced polymer composite panels bonded to the exterior surfaces of a steel monopole tower to strengthen the tower are disclosed in U.S. Pat. Appln. Pub. No. US2003/0010426. Various ways of covering the tower are shown.
U.S. Pat. Appln. Pub. No. US2003/0026923 discloses semi-circular sleeves to enclose and reinforce a monopole tower. In one embodiment, a compressible material is snugly fitted between the sleeve and the tower to transmit shear forces between the tower and the sleeve.
Historically, earlier utility towers of reinforced design are shown in U.S. Pat. No. 811,435 and U.S. Pat. No. 4,216,636 wherein a plurality of rods and connectors are used in open lattice patterns to construct the towers. An open lattice tower construction is shown in U.S. Pat. No. 854,366 wherein the open lattice surrounds and supports an insulated conduit therein. U.S. Pat. No. 1,786,631 discloses an early monopole utility tower with features to insulate the electric cables within the tower.